PLAGL2 Upregulation Transcriptionally Activates OLFM4 to Promote the Malignant Progression of Bladder Cancer through STAT3 Signaling

Abstract

Background: Bladder cancer is the most ordinary malignant tumor of the urinary tract globally. As a transcription factor, pleomorphic adenoma gene like-2 (PLAGL2) is overexpressed in many malignancies, including bladder urothelial carcinoma. This study aimed to explore the effects of PLAGL2 on the malignant progression of bladder cancer and the molecular mechanism related to the downstream gene Olfactomedin 4 (OLFM4). Methods: Western blot was applied for the estimation of PLAGL2 and OLFM4 expression in bladder cancer cells. After PLAGL2 or OLFM4 silencing, cell viability and cell proliferative capability were evaluated utilizing cell counting kit-8 (CCK-8) and 5-ethynyl-2′-deoxyuridine (EDU) staining. Cell apoptosis and stemness were tested by Terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) staining and tumor sphere formation assay. JASPAR database predicated that PLAGL2 could bind to OLFM4 promoter region, which was confirmed by luciferase reporter assay and Chromatin immunoprecipitation (ChIP) assay. Subsequently, the rescue experiments were conducted by OLFM4 overexpression or signal transducer and activator of transcription 3 (STAT3) activator treatment in PLAGL2-silenced bladder cancer cells. Results: Highly expressed PLAGL2 (p < 0.01 or p < 0.001) and OLFM4 (p < 0.01 or p < 0.001) were observed in bladder cancer cells. PLAGL2 or OLFM4 silencing suppressed the proliferation, promoted the apoptosis and alleviated stemness of bladder cancer cells (p < 0.001). Additionally, PLAGL2 could transcriptionally activate OLFM4 and regulate OLFM4 expression to affect STAT3 activation (p < 0.001). Rescue experiments suggested that OLFM4 overexpression or STAT3 activator restored the impacts of PLAGL2 interference on cell proliferative capability and cell apoptotic level in bladder cancer (p < 0.01 or p < 0.001). Conclusion: Collectively, this study demonstrated that PLAGL2 drives the advancement of bladder cancer via modulating the transcriptional activation of OLFM4 to regulate STAT3 signaling. This finding might provide a new sight for the mechanism underlying bladder cancer and reveal PLAGL2/OLFM4 as candidate targets for bladder cancer therapy.